Portable electronic devices that use rechargeable batteries are well known. Such devices include, but are not limited to, smart phones, cellular phones, MP3 players, portable gaming systems, portable computers (e.g., laptop computers, notebook computers, netbook computers, palmtop computers, and tablet computers), wireless reading devices (e.g., the AMAZON KINDLE), and battery-powered tools. The continued use of such devices requires that their batteries be periodically recharged. The procedures for recharging the particular batteries depend upon the chemistries of the batteries. For example, batteries with a nickel-cadmium (NiCad) chemistry require a different recharging process than do batteries with a lithium-ion chemistry.
Portable electronic devices typically use a single processor to handle primary functional features of the device, as well as battery charging. Thus, the single processor often requires a substantial amount of power just to boot up (e.g., on the order of 20 milliamp-hours (mAh) at 3.25 volts for a typical smart phone). Such start-up power requirements dictate the minimum level of charge required in the battery for the device processor to boot reliably.
After a battery has been discharged to the point where it can no longer supply sufficient power for the device processor to boot up, the battery must be recharged for a sufficient length of time to achieve a minimum voltage level that insures that the battery can meet the boot up power requirements of the device processor. Such a minimum voltage level is typically referred to as the “cutover voltage” and the recharging process is typically referred to as “recovery.” Once the battery has recovered and the cutover voltage has been attained, the battery can supply the processor sufficient power to boot up and begin device operation. The cutover voltage is typically pre-programmed into device memory based on the chemistry or type of the battery originally intended for use in the device.
However, as battery technologies evolve, battery chemistries change. Therefore, depending upon how long a portable electronic device remains in use and how fast battery technology changes, a battery with a newer technology, and possibly the ability to supply processor boot up power at a voltage lower than the pre-programmed cutover voltage, may be used with a device. For example, lithium-ion batteries are currently transitioning from chemistries, such as lithium cobalt oxide (LCO), with end of life voltages of at least three volts to lower voltage (LV), higher energy density chemistries with end of life voltages of less than three volts. As a result, when an LV battery is used in a portable electronic device originally designed for use with an LCO battery, the charging time required to attain a pre-programmed cutover voltage above three volts would increase dramatically because the LV battery fully recovers at less than three volts. An example of the dramatic increase in charging time is illustrated in FIG. 1, which depicts a graph 100 of recovery time versus battery voltage for exemplary LV and LCO batteries recharged in a portable electronic device designed for use with the LCO battery, when the state of charge for each battery is 2.75 volts and the processor of the portable device boots up at 3.25 volts. As shown, the LCO battery recovery curve 102 illustrates that the LCO battery recovers to 3.25 volts in about nine minutes; whereas, the LV battery recovery curve 104 illustrates that the LV battery recovers to 3.25 volts in about thirty minutes, which is more than three times longer than the LCO battery recovery. Therefore, because portable electronic devices are not presently designed to adapt battery recovery processes to accommodate different battery chemistries or types, battery recovery can be undesirably long when new, more efficient battery types are used in devices originally designed for older, less efficient battery types.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated alone or relative to other elements to help improve the understanding of the various embodiments of the present invention.